Surface nonuniformity

The interaction between PFPEs and disk overcoat is another significant factor to affect the properties of lubricant films. PFPEs with functional endgroups (e.g., Zdol and Ztetraol) perform better than PFPEs with nonfunctional endgroup (e.g., Z03) for retention and evaporation at the expense of the surface mobility or replenishment ability. However, strong endgroup functionality can lead to the layering and instability (e.g., surface nonuniformity/dewetting) of PFPE films (Karis... 

The importance of surface area in colloidal chemistry has spurred many attempts to develop a method of its accurate measurement from physical adsorption processes. All of the methods so far are empirical and attended with difficulty involving surface nonuniformity, polymolecularity, conformational shifts, and multilayer adsorption. Polysaccharide surfaces are seldom... 

Although the role of surface nonuniformity in catalytic kinetics has been acknowledged by many researchers, a limited number of investigations has sought to quantify its impact on observable kinetics. Quantitative analysis of catalytic processes has advanced significantly by consolidating experimental, theoretical and semiempirical information via microkinetic analysis... 

SURFACE NONUNIFORMITY APPROACHES IN CATALYSIS PRESENT STATE OF KNOWLEDGE... 

Contact of dust particles may take place when they mesh with surface nonuniformities (adhesion) or particles deposited previously (autohesion). A band of adherent particles is first formed and this continues to grow until the entire surface is covered. Photomicrographs show that the particles are caught and held primarily on surface irregularities. Not all of the particles that come into contact with the surface will adhere to the surface. Fora fine fraction of dust, the adherent particles are mainly in the 2-3-jLtm size range, even though the particles suspended in the air have sizes up to 12 jum. 

The structural features of mixed oxides with a mosaic surface of nanoparticles, including patches of different oxide phases or a solid solution of a lower concentrated oxide in a more concentrated oxide, can strongly affect the interfacial phenomena in any media. For instance, the enthalpy of immersion in water (Table 2.1 is greater for mixed nanooxides than nanosilica. However, surface nonuniformity and the differences in the properties of a variety of surface sites result in a significant scatter in the relationship between the and 5bex values (Figure 2.1), despite a tendency of a decrease in the AH value (calculated per surface area unit) with increasing value. 

In Figure 8, for the neutrally-wetted system there is evidence of a widening of the range of possible contact angles and the development of a bimodal functionality for the roughest surfaces investigated. This behavior could have depended on the surface saturation history or on the presence of local surface nonuniformities and was not pursued. 

The first treatment of the influence of surface nonuniformity on kinetic behavior was that of Constable [1]. He considered the surface to be composed of different sites of the i-th type, with ni representing the number of sites of type i with an activation energy of E,. The overall rate constant is then, if the preexponential factor is assumed invariant ... 

For horizontal surfaces, anodes without overlay can be recessed in the concrete surface. Nonuniform current distribution is a fundamental concern in these systems. Anodes in the form of a titanium mesh, with proprietary surface coatings of precious metals are commonly used in concrete structures, in conjunction with cementitious overlays. These systems are applicable to both horizontal and vertical surfaces and generally provide uniform current distribution. 

Pressing the molten or softened surfaces is used to deform surface asperities and expel entrapped gases from the joint area to produce intimate contact at the interface. The process can be described and modeled as squeezing flow of viscoelastic fluids [2]. It entails flow at the microscale to deform asperities, and at the macroscale where melt squeezes out of the joint area forming weld flash. However, a complete description of the process is quite complicated due to the complex melt behavior, irregularity of the joint surfaces, nonuniform temperature field, and air entrapment. It is also important to note that additives or reinforcements can increase the effective viscosity of the melt, making the flow slower. 

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